If fish does protect the aging brain, researchers believe that the benefits probably come from the omega-3 fatty acids found most abundantly in oily fish like salmon, mackerel and albacore tuna.

Lab studies show that omega-3 fats have a number of properties that could help stave off dementia -- including actions that protect nerve cells, limit inflammation and help prevent the build-up of the amyloid proteins seen in the brains of Alzheimer's patients.

These latest findings are based on surveys of 14,960 adults age 65 or older living in China, India, Cuba, the Dominican Republic, Mexico, Peru or Venezuela.

It’s true. Fish is high in brain-building fat, but Dr. Fuhrman points out most varieties of fish—especially tilefish and mackerel—are heavily polluted with mercury. Dr. Fuhrman’s DHA Purity is a contamination-free omega–3 fatty acid supplement, but if you must have fish, here’s Dr. Fuhrman’s opinion on it.

We are finding out each year that fish is even more polluted than we thought. Even farm raised fish not only contains mercury, but other chemicals, antibiotics and algaecides that are potentially risky for us and the environment. Of course, we have to avoid the high mercury fish such as swordfish, mackerel, pike, shark and even tuna, but the farm-raised fish is not harmless or a health food either.

Though fish is touted as a health food, because of its lower levels of saturated fats and higher omega-3, the reality is that most of the fish available in the market today is farm-raised and does not have significant amounts of omega-3, and neither should it be considered health food. Consuming too much fish has clear risks. Instead, restrict your fish consumption and assure omega-3 adequacy with either an algae-derived DHA supplement, plus walnuts and ground flax seeds, or take a purified fish oil (certified to be contamination free). I of course would prefer people take the plant-derived DHA (cultivated for this purpose), and not harm our oceans, the wildlife, and pollute the natural habitats trying to feed the world with fish-derived omega-3.